This appln. is a 371 of PCT/DE95/01163 filed Aug. 18, 1995.
The invention relates to liposome-encapsulated taxol, its preparation and its use. Areas, in which the invention can be used, are medicine and the pharmaceutical industry.
Taxol is a natural product, which occurs in the bark of various species of yew (Taxaceae) and can be obtained from these barks (J. Amer. Chem. Soc., 93:2325 (1971)) or recently also by chemical synthesis (J. Amer. Chem. Soc., 1110:5917-5919 (1988)). Compared to previously known cytostatic drugs, taxol has a completely novel mode of action (Ann. N.Y. Acad. Sci. 466:733-744 (1986); Sartorelli, A. (ed.): Molecular Actions and Targets for Cancer Chemotherapeutic Agents. Academic Press, New York, 1981, pp. 483-507). The substance promotes the polymerization of microtubuli from tubuli dimers and stabilizes the microtubuli by inhibiting their depolymerization. Furthermore, there is an abnormal arrangement and bundling of microtubuli during the whole of the cell cycle, which leads to the formation of multiple, microtubular dividing stars during mitosis and, with that, to inhibition of the normal dynamic reorganization of the microtubular network. Since the vital cell function in the interphase and during mitosis are decisively affected thereby, taxol exhibits clear antineoplastic activity against different tumors, also implanted B16 melanoma and P388 leukemia and against human breast tumors.
The applicability of taxol is greatly limited by its low water solubility. Solubilizers, such as Cremophor (polyethoxylated castor oil) and alcohol improve the solubility but, when used, lead to appreciable side effects, such as anaphylactoid reactions. The dilution of such solutions with physiological salt solution for the administration has the disadvantage that the stability of taxol in physiological salt solution is inadequate (not more than 24 hours). A dose-limiting side effect is myelosuppression and, primarily, neutropenia (Semin. Oncol. 19:646-662 (1992). Because of their amphiphilic character, liposomes offer the possibility of encapsulating or incorporating water-soluble as well as lipid-soluble substances.
As a substance almost insoluble in water, taxol can be dissolved with high efficiency in the lipid phase of liposomes of suitable composition, so that the toxicities, due to Cremophor EL and observed in man, including an increased formation of chylomicrons, should no longer occur. The therapeutic effectiveness of free, liposome-encapsulated and nanoparticular taxol was compared in vitro on two leukemias, P388 and L1210. While the growth of P388 cells was inhibited equally by all three forms of the drug, L1210 exhibited a greater sensitivity towards the nanoparticular form.
When all 3 preparations were tested in vivo on P388 (12.5 mg/kg/4 days), the free and liposomal forms were comparable in their therapeutic effectiveness, while nanoparticular taxol caused acute toxicities (J. Microencapsul. 7 (2) 191-7 (1990)). In a further study, taxol was tested in the free and liposomal form with regard to the antitumor activity on two human glioblastoma in the nude mouse model (12.5 mg/kg/4 days). Both forms resulted in a significant decrease in tumor growth (in vivo 6 (1): 23-7, (1992)). Sharma et al. (Cancer Res. 53, 5877-81 (1993)) and Straubinger et al. (J. Natl. Cancer Inst. Monographs 15, 69-78 (1993)) reported that liposomal taxol (10-45 mg/kg) had a significant antitumor effect on the murine taxol-resistant colon-26 model. The encapsulation of taxol in liposomes and the use of the products obtained for the treatment of carcinoses is described in WO 93/18751. A combination of this treatment with hyperthermia is preferred. The taxol liposomes produced exhibit improved stability.
Previously, a patent application (WO 93/18751) was filed, in which a plurality of combinations of taxol and liposomes is claimed, of which, in particular, vesicles with a positive charge and based on cardiolipin, phosphatidyl choline and cholesterol were produced and investigated. However, the taxol, encapsulated in this manner, had to be administered on four consecutive days in the animal experiments, since a single administration evidently did not lead to the desired antitumor effect.